Experiments are designed: 1) to examine the extent of neural influence on consecutive segments of pre and postcapillary microvessels; 2) to analyze the degree of interaction between nervous and myogenic controls mechanisms and explore the influence of the cognate tissue metabolic condition on the above control mechanisms; 3) to evaluate biologically and by radio-enzymatic-assay methods, the amount of neurotransmitter effectively reaching precapillary vessels. The experimental approach involves the use of (1) isolated nerve-intact artificially perfused mesoappendix and striated muscle vasuclatures of the same tissues and species. The former preparations will serve: (a) to quantitate the extent of microvessel response to neural activation reflexly or by electrical stimulation: (b) to evaluate the degree of interaction between neural and myogenic control mechanisms by shifting microvessel transmural pressure; and (c) to determine the amount of addrenergic nerve transmitter present in venous effluent. The latter tissue preparations will be used to evaluate the influence of parenchymal tissue metabolic condition on vessel response. The possibility of participation of adrenoreceptors, and of other (cholinergic, histaminergic) receptors, in precapillary microvessel control will be determined by the use of appropriate specific blockers. In these experiments, quantitative indices of microvascular behavior, i.e., number and diameter of arterioles, cell velocity in arterioles and venules, and number of perfusing capillaries (density) during steady-state and during nerve activation will be correlated with other simultaneously-secured quantitative indices, i.e., hemodynamic (pressure, venous outflow, resistance) and metabolic consequences (e.g., oxygen consumption) of the cognate tissue. 4) We will continue to study: (a) the resonse of cerebral vasculature to rising systemic arterial and venous pressure, as measured by the transit time of a marker (cortical) and measurement of changes in diameter of selected pial pre and postcapillary microvessels: b) extend our investigation of the contribution of nucleous locus coeruleous (LC) to the regulation of cerebral microcirculation. Some of these quantitative determinations in cerebral microcirculation will be done under known level of anesthetics and controlled respiratory conditions.